1. Field of the Invention
The present invention relates to a process for the preparation of mono alkyl aromatic compounds.
2. Brief Description of the Related Art
Benzene and other aromatic hydrocarbons are readily alkylated with olefins using a catalyst comprising a fluorinated sulphonic acid being supported on polar porous contact material. U.S. Pat. No. 5,959,169 discloses a process to remove aromatic hydrocarbons from a hydrocarbon mixture by selective alkylation of the noxious unsubstituted aromatic compounds with an olefinic alkylating agent in the presence of a catalyst consisting of a fluorinated alkyl sulphonic acid on a silica containing support material.
In a mixed stream of hydrocarbons containing aromatic compounds it is desirable to achieve high conversion with maximum selectivity to mono alkylated products. However, the alkylation reaction produces not only the desired mono alkylated product, but also products in which two or more alkyl groups are introduced. This problem is particularly important under conditions with high conversion of the aromatic feedstock.
It has been observed that fluorinated sulphonic acids including trifluoromethanesulphonic acid supported on a polar porous support material are capable of catalysing trans-alkylation reactions in which the poly-alkylated aromatic by-products are reacted with non-alkylated aromatic compounds to produce mono-alkylated aromatic compounds.
In accordance with the above finding, this invention is a process for the mono-alkylation of a aromatic hydrocarbon substrate in presence of a fluorinated sulphonic acid by contact of the aromatic substrate with an alkylating agent consisting of a mixture of olefinic compounds and poly-alkylated aromatic compounds.
The process according to the invention is in particular useful in the removal of benzene from reformat gasoline. With the tightening specifications on benzene content of gasoline it is desirable to convert benzene to less noxious alkyl derivatives such as ethyl or isopropyl benzene. These compounds have high octane numbers and alkylation of benzene to these compounds increases the octane value of the product. Poly-alkylated benzene being employed in the inventive process as alkylating agent such as tri-isopropyl benzene or triethyl benzene boil at temperatures being outside the range of compounds to be desirable to include those compounds into gasoline.
In the following examples the invention will be disclosed in more detail.